Conventional chaffer slats have been made from a relatively long sheet metal strip punched along the top edge of the sheet to form spaced teeth of the sieve portion of the slat and the bottom portion of the metal strip below the teeth is folded upon itself and then its edge margin is inwardly rolled to form a passage for the slat supporting rod. This folded portion is then bent backwardly to bear the rolled edge against the back side of the slat to form the air blast baffle. The rolled edge of this doubled portion of this slat serves to catch and interrupt the downward flow of the grain so that considerable amounts of the separated grain are trapped or deflected into the upwardly flowing air stream and decreases the efficiency of the chaffer operation. A conventional chaffer and sieve construction employing slats of this kind is shown in U.S. Pat. No. 2,253,296, and it was the efforts to cure this problem, simplify manufacture and reduce production costs that resulted in the present invention.